Observational issues in radiometric and interferometric detection and analysis of the Sunyaev-Zel'dovich effects

Radiometric observations using single dishes and interferometers are responsible for most detections of the Sunyaev-Zel’dovich (SZ) effects. This article discusses the techniques used in measuring the thermal and kinematic SZ effects in this way, the pitfalls that may arise, the systematic errors in the data, and the resulting uncertainties in the interpretation of the results. Since these uncertainties limit the physics return from SZ effect research, some approaches that would improve this situation are described. Longer reviews of SZ effect research (Rephaeli 1995; Birkinshaw 1999; Carlstrom, Holder and Reese 2002) may be consulted for additional details. 1 . 1. Radiometric quantities. – In discussing radiometric observations it is conventional to work with the flux density (S�, the energy received per unit time per unit frequency per unit area) as the measure of the brightness of an unresolved source. However, the SZ effects of clusters of galaxies are extended, and so a measure of surface brightness is more appropriate. Two such quantities are in general use. The flux density per unit solid angle, ��, is commonly adopted in describing interferometric observations, where the solid angle is usually the area of the synthesized beam. The brightness temperature, TRJ, is more usual in single-dish work. Flux density per unit solid angle and brightness temperature are related by